Pressure-resistant vessel

ABSTRACT

A wheel-shaped pressure-resistant vessel for storing gaseous, liquid or liquefied fuel and which has a substantially rigid shape. Specifically, the vessel contains a substantially continuous shell of a fiber-reinforced resin. The shell has a central opening, an inner lining and an axial reinforcement member. The shell has a substantial mechanical equilibrium shape such that the axial member is situated in a central opening. The axial member contains an inner member and two end plates, with each of the end plates fixing the shell to the inner member. Further, the axial member is attached, through both end plates, to the shell such that outer surfaces of the shell are pulled towards each other, thus reinforcing the vessel and maintaining the vessel, even while it is pressurized, in its wheel-like shape.

The present invention is directed to a pressure vessel for gaseous,liquefied or liquid materials and the like.

Pressure resistant vessels have been in use for numerous applications,one of them being the use as an LPG-container for automotive purposes.LPG is an interesting fuel for automotive purposes, i.a. due to the lowprice and low emission of environmentally harmful substances; hence, itsuse thereof has increased substantially over the last decades. However,LPG is a material that has been liquified through pressurization, withthe consequence that the requirements for safety are very high. In viewof their relatively low costs, generally steel pressure tanks are usedfor storage of LPG, the pressure tanks generally being substantiallycylindrical and having torispherical domes.

A distinct disadvantage of these LPG containers is their weight and theamount of space they require in a car. In the smaller (compact) carsthis weight and especially the amount of space required makes the use ofLPG, as fuel, rather unattractive.

It is an object of the invention to provide a pressure vessel having arelatively low weight, and a shape which makes it better suitable forautomotive applications. Another object is to provide a pressure vesselwhich may be used by a person carrying the vessel, for example on theback.

The invention is based on the development of a wheel shaped vessel,which vessel may have the size of a spare car wheel and which will fitin the area provided for the spare wheel.

The invention is accordingly directed to a wheel shaped pressureresistant vessel for gaseous, liquid or liquefied material having asubstantially rigid shape, the vessel comprising a substantiallycontinuous shell of a fiber reinforced resin having a central opening,an inner lining and an axial member, the substantially continuous shellhaving a substantial mechanical equilibrium shape, whereby the axialmember is present in the central opening of the shell.

A preferred embodiment of the invention provides a wheel shaped pressureresistant vessel, comprising a substantially continuous shell of a fiberreinforced elastomeric resin having a central opening, a gas tight,substantially rigid inner lining and an axial member, the substantiallycontinuous shell having a substantial mechanical equilibrium shape,whereby the axial member is present in the central opening of the shelland is attached to the rims of the central opening, thereby closing thecentral opening.

The shell is comprised of a fiber reinforced resin body. The fibers havebeen wound along substantially geodetical lines, and the shape of avessel is designed so that the load is substantially equal everywhere inthe fibers (more or less isotensoid). Preferably a combination ofrelatively stiff fiber re-inforcement and flexible matrix material ischosen, resulting therein, that the design, production and use of thevessel is very tolerant of deviations and stress-concentrations.Deviations of geodetics and/or continuity become possible to a certainextent, provided the structural integrity is maintained.

The so-called “netting” theory has been used for this design. Thistheory assumes that in case of the use of stiff fibers in a non-rigid(such as elastomeric) matrix, the influence of the matrix may bediscounted for calculating the forces in a system of fibers of a woundconstruction. This theory is valid when the stiffness of the matrix isnegligibly small compared to the stiffness of the fibers. A theoreticalreport on the development of pressure bodies using the netting theorycan be found in the report of the Technical University of Delft, TheNetherlands, report VTH 166 (the “VTH-166 report”), which isincorporated herein by reference.

Winding the substantially continuous fiber reinforcement along asubstantially rotation symmetrical body results then in an equilibriumshape that is non-spherical, preferably approximately elliptical, anddetermined by the form parameter q as defined in the VTH-166 report. Inview of the applicability of analytical methods, such as the nettingtheory to the present invention, which is justified by the difference instiffness between the fibers and the matrix, the use of continuousfibers for the winding of the body will lead to the situation where thetension in all the fibers is substantially equal throughout the body(isotensoid).

The shape and size of the vessel is determined by the followingdifferential equation (See also FIG. 1)$\frac{X}{Y} = {{\pm \frac{\sqrt{{a^{2}\left( {Y^{2} - 1} \right)} - \left( {Y^{3} + {kY}} \right)^{2}}}{Y^{3} + {kY}}}\quad {wherein}}$${X = \frac{x}{y_{0}}},{Y = \frac{y}{y_{0}}},{a = \frac{n\quad F}{\pi \quad {py}_{0}^{2}}},{k = \frac{K}{\pi \quad {py}_{0}^{2}}}$

F Tension force in the fibres

K axial load on the poles of the vessel

X,Y dimensionless co-ordinate axis

x,y co-ordinate axis

a constant; describes relation between internal pressure and number offibers

k constant; describes relation between internal pressure and polar load

n number of yarns in cross-section

p internal pressure

y₀ polar opening radius

An inflatable body of a somewhat comparable shape has been disclosed inEP-A 626,338, the contents of which is incorporated herein by reference.The essential differences between this known body and the presentinvention are, among others, the requirement of a rigid shape,preferably provided by the lining and the axial member.

The vessel of the present invention may have different constructions,depending on the materials used and the actual requirements on the size,shape and strength.

An essential requirement is that the vessel is rigid. This means, thateither the shell is rigid, or that the inner lining is rigid. In thiscontext the term rigid is understood to mean, that without internalpressure, the shape of the vessel is substantially maintained.

The shell, prepared from fiber reinforced resin, can either be rigid orflexible. In a preferred embodiment the shell is prepared from anelastomeric resin, such as a vulcanised or thermoplastic rubber.

The inner lining may also be rigid or thermoplastic. In case the shellis flexible it is essential that the lining is rigid. Otherwise, theselection may be made based on criteria of construction and gaspermeability.

The axial member may have two functions in the pressure vessel accordingto the invention. In the first place this member may provide thenecessary means for attachment of all accessories or appliances that arerequired for the actual use as a pressure vessel, e.g., a valve forfilling/emptying the tank and, if desired, apparatus for measuringpressure of the fuel contained within the tank and/or determining adegree to which the tank is filled with fuel; and. It is for examplepossible to accommodate all said means inside the axial member, or ontop thereof. In the second place, and this is much more important, theaxial member provides the necessary axial reinforcement of the vessel,by providing a link between the two surfaces of the shell, thus closingthe vessel, and pulling the two surfaces together. This latter effect isvery important in terms of the shape of the vessel. Without the link theshape would become too much of a balloon to be suitable for use.

This axial member may be provided by a separate element, such asdisclosed in FIGS. 2 a and 4, or by winding the fiber reinforcementthrough the opening in the vessel.

According to a preferred embodiment the axial member does not extendbeyond planes defining the outermost surface of the shell of thepressure vessel. Thereby the rim of the central opening in the shell ispulled inward, thus creating an actual wheel like shape.

The vessel body has a geometrically continuous shape and substantiallyno stress concentrations occur, with the exception in the area where theaxial reinforcement member holds the two surfaces together. The shape ofthe body contains substantially no discontinuities in the mathematicalsense, with the exceptions discussed above.

To enable the vessel to hold gases or liquids, a gas-tight inner liningis present. This lining is preferably substantially rigid, thusproviding the required shape to the pressure vessel. The material of theinner lining will be selected in relation to the intended application.Of course the material has to be gas tight at the thickness used, whichmeans that an amount of gas passing through it should not exceed thecriteria of the applicable laws and regulations. Suitable values thereofare less than 10 ml/h, independent of surface area.

Furthermore, the material must be resistant to chemical influences ofthe gas or liquid. Finally, it must be able to withstand externalforces, that could be exerted on the vessel, such as crash-loads,penetration, indentation and the like. Suitable materials for the innerlining are e.g, the various non-elastomeric ethylene and propylenepolymers, PVC and copolymers, as well as metals, such as steel oraluminium.

To protect the vessel against foreign objects, damage, wear,environmental influences, chemicals, such as oils, acids, lye, fats andthe like, a protective outer lining may be used. Preferably, this outerlining is able to withstand mechanical and thermal abuse without earlycollapse.

The pressure vessel according to the invention may be used as an LPGcontainer for automotive use, as discussed hereinabove, but also forother applications wherein pressure vessels can be useful. Examplesthereof are lightweight, crash resistant pressure vessels, for examplefor holding hazardous gases or liquids under high pressure, such asgaseous, liquefied or liquid propellants in the aerospace industry.Other applications can include storage of oxygen or air for rescueworkers, fuel for cooking or other equipment, cryogenic storage(provided a suitable isulation is present, for example in the form of afoam between two walls in a double walled vessel), fire extinguishingliquids or gases, and the like.

The vessel can be fire proof by the choice of the materials ofconstruction thereof, or by the use of suitable fire proofing additivesor barriers therein.

The pressure that the vessel can withstand depends on the constructionthereof, and more in particular, on the fiber density in the shell.Generally, the vessel can withstand pressures from little aboveatmospheric to more than 100 bar, for example, up to 400 bar.

The fabrication of the fiber reinforced resin body can take place invarious ways. A suitable method is winding a pre-impregnated fiberaround the rotation symmetric core (for example the rigid inner lining),optionally followed by further impregnation of the final fiberreinforcement with the resin and solidification and/or vulcanization.However, it is also possible to apply a resin matrix to thesubstantially rotation symmetric core prior to the winding of the fibersand/or after the winding of the fibers. After the fiber reinforcementhas been wound around the core, the core is removed. This can be done byusing a core that collapses in parts, by a temporary core composed ofloosely bound solids, a core of hardened glass, which may be broken andremoved after production, or an inflatable core.

In order to provide the required shape in the area of the inner rim ofthe shell, the shape of the lining preferably deviates somewhat from thetheoretical equilibrium shape. As has been shown in FIG. 3, the surfaceextends somewhat outwardly, thus enabling the attachment of the axialmember, after the extending part has been inverted inside.

After the fiber reinforcement body has been wound, woven or braided, itcan be incorporated in a resin matrix. It is also possible to windresin-impregnated fibers, which results in the forming of the resinmatrix. In a preferred embodiment, the shell is produced by firstapplying a layer of resin material on the body, preferably an elastomer,subsequently winding one or more layers of fibers (strands) around thisbody, preferably two layers, and finally again applying a final layer, aresistance layer, over the final layer of fibers.

The matrix can then be solidified, for example by vulcanization.

The fiber reinforcement can be constructed from various materials,generally comprising natural or synthetic organic or inorganic fibers,although the well-known aramid fibers, such as Kevlar (TM) and Twaron(TM) are suitable choices. Those fibers provide sufficient tensilestiffness in combination with strength. Other suitable fibers are allthose fibers with a high tensile strength and/or stiffness, like sisal,carbon fibers, E-, R- and S-glass fibers, and those polymeric fiberswhich are suitable in the environments where the vessels are used, suchas the high molecular weight polyethylene fibers, polyester fibers andother fibers from high quality plastics (engineering plastics).

The matrix resin material of the shell may be elastomeric or rigid.Preferably, the shell is prepared from a fiber reinforced resin selectedfrom the group of elastomeric, thermoplastic elastomeric, thermosettingand thermoplastic, non-elastomeric resins. As to the elastomer matrix,any suitable elastomer can be used, although it is preferred that a highquality elastomer having a good resistance against environmentaldegradation, such as ozone resistance, is used. Suitable elastomers are,for example, the isoprene, polyurethane, styrene-butadiene,butadiene-nitrile, EP(D)M, polybutadiene and silicone elastomers, whichare optionally vulcanized after the body has been shaped. The mostpreferred elastomer, especially for use as an LPG container ischloroprene rubber.

The invention is elucidated on the basis of the following figures,without being restricted thereto.

In FIG. 1 the principle equation for designing the vessel, together witha schematic drawing showing some of the variables, is given. In FIGS. 2^(a-c) the principle of preparing the shell of the vessel is shown. FIG.3 gives the X-Y relation in the wound (equilibrium) shape and the finalshape, after insertion of the axial member.

In FIG. 4 the construction of part of the assembled vessel with separateaxial member is given. The end plate 1, provided with valve 2, isattached by means not shown to axial reinforcement member 3 and to endring 4. Thereby, a cylindrical enclosure is formed inside the centralpart of the shell, the rims of which are held in place between the endplate 1 and end ring 4.

FIG. 5 depicts a cross-sectional view of the assembled vessel, in itsentirety. As shown, end plates 1 secured to each other throughreinforcement members 3 abut against rims on outer surfaces of thevessel. Axial reinforcement members 3, together with both end plates,for a centrally-located co-axially oriented cylindrical structure withinthe vessel, the vessel having inner lining 5 and outer resin reinforcedshell 6. Fill valve 2, through which the vessel can be filled and adegree to which the vessel is filled can be determined, and pressuregauge 7, for measuring pressure of the LPG within the vessel, aremounted to an upper one of end plates 1. The rims are held in placebetween end plates 1 and end rings 4.

What is claimed is:
 1. A wheel-shaped pressure-resistant vessel forstoring gaseous or liquid pressurized fuel, the vessel having asubstantially rigid shape and comprising: a substantially continuousfiber-reinforced shell formed of a flexible fiber-reinforced resin; acentral opening; a gas-tight, substantially rigid inner lining; and anaxial reinforcement member, the axial reinforcement member having adevice through which the vessel can be filled with the pressurized fuelor emptied of the fuel; wherein: the shell has a substantial mechanicalequilibrium shape when the vessel is in a non-pressurized condition suchthat the axial reinforcement member is present in the central opening;the axial reinforcement member comprises an inner member and two endplates, each of said end plates fixing the shell to the inner member;and the axial reinforcement member is abuttingly attached through theend plates to opposing outer surfaces of the shell such that the outersurfaces of the shell are pulled towards each other, wherein, once thevessel is fully pressurized with the fuel, the shell substantiallyretains the equilibrium shape.
 2. The vessel recited in claim 1 whereinthe axial reinforcement member is situated in the central opening of theshell and is attached to rims of the central opening so as to close thecentral opening.
 3. The vessel recited in claim 1 wherein a ratio of adiameter of the central opening to an outer diameter of the vessel lieswithin a range of greater than or equal to 0.1 but less than 1.0.
 4. Useof the vessel recited in claim 1 as an LPG-container for automotivepurposes.
 5. The vessel recited in claim 1 wherein the axialreinforcement member further comprises means for determining pressure ofthe fuel contained in the vessel.
 6. The vessel recited in claim 1wherein the axial reinforcement member further comprises means fordetermining a degree to which the vessel is filled with the fuel.
 7. Thevessel of claim 1 wherein the fiber reinforced resin comprises anelastomeric resin.
 8. The vessel of claim 1 wherein the fiber reinforcedresin comprises a non-elastomeric resin.
 9. The vessel of claim 1wherein the fiber reinforced resin comprises a thermoplastic resin. 10.The vessel of claim 9 wherein the fiber reinforced resin comprises athermoplastic-elastomeric resin.
 11. The vessel of claim 1 wherein thefiber reinforced resin comprises a thermosetting resin.
 12. The vesselof claim 11 wherein the fiber reinforcement of the shell comprisesfibers selected from the group of polyamide fibers, polyolefinic fibersand aramide fibers.
 13. The vessel of claim 1 wherein the fiberreinforcement of the shell comprises inorganic fibers.
 14. The vessel ofclaim 1 wherein the fiber reinforcement of the shell comprises carbonfibers.